FIG. 1 shows a conventional air filter device which is used for the same purpose as the present invention. Referring to FIG. 1, the conventional air filter device 100 includes a main body 101 which has an air inlet port 102 and an air outlet port 103, and a filter cartridge 104 which has a casing shape and is fastened to the lower portion of the main body 101. Further, a cylindrical filter material 105 is longitudinally disposed in the filter cartridge 104. Air fed through the air inlet port 102 flows downwards into the filter cartridge 104, and passes through the filter material 105 to be fed into hollow portions formed in the filter material 105. Afterwards, the air flows upwards and is discharged through the air outlet port 103 (see, the arrows). While the air passes through the cylindrical filter material 105 and flows into the hollow portions 106, the air is filtered.
As such, the conventional air filter device 100 is useful to filter air. However, the shape and the coupling structure of the filter cartridge 104 and the filter material 105 increase the total volume of the air filter device 100, so that it is inconvenient to manufacture and install the air filter device 100, and it is uneconomical.
Further, another air filter device 110, which has a simpler structure, has been proposed. As shown in FIGS. 2 and 3, the air filter device 110 includes a housing 111. An air inlet port 112 and an air outlet port 113 are formed in opposite sides of the housing 111. The interior of the housing 111 is filled with a filter material 114. A plate 115 covers the housing 111. However, the filter material 114 is not efficiently used because excessive filtering is performed at a position adjacent to the air inlet port 112.